The telecommunications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have a high bandwidth, thereby allowing more information to be carried than with copper wire.
Telephone communications require full duplex communications, wherein each station on a communications channel can transmit and receive with apparent simultaneity. For example, an ordinary telephone provides full duplex communications; a user can talk and listen at the same time.
When servicing a fiber optic cable during installation or repair, field service personnel tap into the cable with a talk set. This enables communication between the field service personnel and the central switching station or with other field service personnel, and facilitates the work on the cable. The talk sets behave much like ordinary telephones in that full duplex communications are provided.
Prior art talk sets achieve full duplex communications in clumsy ways. One type of prior art talk set requires two optical fibers connected to each talk set; one fiber is for transmitting and the other fiber is for receiving. Such an arrangement necessitates an extra connection, as well as logistical work in ensuring that one talk set's transmit fiber is connected to the other talk set's receiving fiber. Another prior art talk set uses wavelength division multiplexing, wherein one talk set transmits information at one frequency and the other talk set transmits information at another frequency. Use of such dual frequency talk sets complicates interchanging talk sets. Operators must always ensure that their talk sets are compatible with their listeners' talk sets.
Besides achieving full duplex communication, there is a problem of achieving long range communication over optical fibers. Optical fibers typically impose a 0.3 db/km loss on a signal. At a distance of 100 km, this becomes about a 30 db loss. Prior art talk sets have proven to be unsatisfactory in communicating in this range. Furthermore, long range communication produces reflections of the transmitted light signal off of connectors, splices and the like. When using a single optical fiber and a single frequency to transmit and receive, the reflections from one's own talk set are easily mistaken for the incoming signals from the other talk set and thus interfere with communications.